1. Field of the Invention
The invention relates to a fuel pressure adjusting apparatus which adjusts a pressure of fuel supplied from a fuel tank to an injector of an internal combustion engine by a fuel pump.
2. Description of the Related Art
Japanese Patent Application Publication No. JP(A) 2000-45897 discloses a fuel pressure adjusting apparatus shown in FIG. 8. In the fuel pressure adjusting apparatus 1, an inside of a casing 2 is divided into an atmosphere chamber 4 and a fuel chamber 5 by a diaphragm 3, and a valve element 6 is provided in the diaphragm 3.
When a pressure of fuel introduced into the fuel chamber 5 through a fuel introduction port 8 becomes equal to or higher than a predetermined value, the diaphragm 3 is moved upward against the force applied by a spring 7, and the valve element 6 opens a fuel discharge port 9. When the valve element 6 opens the fuel discharge port 9, fuel in the fuel chamber 5 is returned to a fuel tank (not shown) through the fuel discharge port 9 as shown by an arrow. As a result, the pressure of the fuel supplied to an injector of an internal combustion engine is adjusted to the predetermined value.
However, in such a fuel pressure adjusting apparatus, the diaphragm needs to be provided so that the two chambers, which are the atmosphere chamber 4 and the fuel chamber 5, are formed. As a result, the number of components is increased, and the entire size of the fuel pressure adjusting apparatus is increased. Also, when the valve element 6 opens the fuel discharge port 9 and the fuel flows out through the fuel discharge port 9, the flow of the fuel is contracted, the pressure of the fuel is reduced, vapor is generated in the fuel pressure adjusting apparatus 1.
In order to solve these problems, a fuel pressure adjusting apparatus shown in each of FIG. 6 and FIG. 7 is proposed.
The fuel pressure adjusting apparatus includes a casing 10; a cylindrical member 11, a valve element 12, and a leaf spring 13 which serves as force-applying means. The casing 10 includes a fuel introduction port 14 and a fuel discharge port 15. The cylindrical member 11 having a communication passage 17 is fixed in the fuel introduction port 14 side of the casing 10. The leaf spring 13 having plural communication ports 18 is joined to the fuel discharge port 15 by crimping. When the cylindrical member 11 and the leaf spring 13 are fixed to the casing 10, the valve element 12 is supported between the cylindrical member 11 and the leaf spring 13 such that one end portion of the valve element 12 contacts a valve seat 16 formed at an end portion of the cylindrical member 11, and the other end portion of the valve element 12 contacts the leaf spring 13.
In the fuel pressure adjusting apparatus with the aforementioned configuration, fuel is supplied to the communication passage 17 of the cylindrical member 11 from a fuel pump (not shown). The fuel constantly applies downward force to the valve element 12. The leaf spring 13 constantly applies upward force to the valve element 12. When the pressure of the fuel is equal to or lower than a predetermined value, the valve element 12 contacts the valve seat 16 of the cylindrical member 11, and closes the communication passage 17 of the cylindrical member 11.
When the pressure of the fuel becomes equal to or higher than the predetermined value, the valve element 12 is moved downward, and the fuel in the communication passage 17 is returned to a fuel tank (not shown) through the communication ports 18 formed in the leaf spring 13. FIG. 6 shows an example of the fuel pressure adjusting apparatus in which the valve element 12 contacts a flat surface of the leaf spring 13. FIG. 7 shows an example of the fuel pressure adjusting apparatus in which the valve element 12 is fitted in a center opening portion 19 formed in the center of the leaf spring 13.
In this fuel pressure adjusting apparatus, the diaphragm and the atmosphere chamber do not need to be provided. Therefore, cost and size of this fuel pressure adjusting apparatus can be reduced, Further, since the fuel flows along the surface of the valve element 12 when the valve element 12 opens the communication passage 17, an amount of generated vapor can be reduced.
However, this fuel pressure adjusting apparatus has disadvantages described below. Since the surface of the leaf spring 13 which the valve element 12 contacts is flat in the fuel pressure adjusting apparatus shown in FIG. 6, when the valve element 12 closes the communication passage 17, an axis of the valve element 12 matches an axis of the valve seat 16 due to a self-aligning effect. Thus, it is possible to prevent the situation in which the valve element 12 contacts the valve seat 16 with the axis of the valve element 12 being deviated from the axis of the valve seat 16, and therefore the fuel leaks.
However, since a distance for which the fuel flows until the fuel hits the leaf spring 13 is the same as the diameter of the valve element 12 when the valve element 12 opens the communication passage 17. Therefore, the flow of the fuel become unstable in the vicinity of a low end of the valve element 12. As a result, the valve element 12 vibrates, and noise occurs.
In the fuel pressure adjusting apparatus shown in FIG. 7, the valve element 12 is fitted in the center opening portion 19 provided in the center of the leaf spring 13, and the valve element 12 is in a fixed state. A distance for which the fuel flows until the fuel hits the leaf spring 13 is smaller than the diameter of the valve element 12. Therefore, before the flow of the fuel becomes unstable in the vicinity of the low end of the valve element 12, the flow of the fuel is separated from the valve element 12. Therefore, the vibration of the valve 12 is reduced.
However, since the valve element 12 is fixed in the center opening portion 19, it is necessary to increase accuracy of production and assembly in order to make the axis of the valve element 12 match the axis of the center opening portion 19 when the valve element 12 closes the communication passage 17. However, it is difficult to increase the accuracy of production and assembly in terms of man power and cost.
Therefore, when the valve element 12 closes the communication passage 17, the axis of the valve element 12 may be slightly deviated form the axis of the center opening portion 19. In this case, the fuel leaks, or a contact portion of the valve element 12 partially wears out. Also, in the case where the axis of the valve element 12 is slightly deviated from the axis of the center opening portion 19, an area of an opening portion on the right side of the valve element 12 becomes different from an area of an opening portion on the left side of the valve element 12 when the valve element 12 opens the communication passage 17. As a result, an amount of the fuel flowing out through the opening portion on the right side of the valve element 12 becomes different from an amount of the fuel flowing out through the opening portion on the left side of the valve element 12. Accordingly, the valve 12 vibrates and abnormal noise occurs when the valve element 12 opens the communication passage 17, as well as in the case of the fuel pressure adjusting apparatus shown in FIG. 6.
Also, in the case where the axis of the valve element 12 is deviated from the axis of the center opening portion 19, when the valve element 12 opens the communication passage 17, the control pressure drops at low flow rates as shown by black triangles and black squares in FIG. 5, that is, the fuel flows out at a pressure equal to or lower than the predetermined value.